Reducing Straight Connector

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We maintain control over the whole process from initial tool design and tool making through to the final assembly and testing. This ensures that only products of the highest quality are produced.

The company believe that it is this commitment to quality that has led to it receiving prestigious awards from many of the world’s leading testing and approvals organisations.

UKAS Management BSI-9001-Drinks UKAS Environmental FDA Food Award

NOTE: For information on approvals and accreditations pertaining to an individual product or product range please refer to our Technical Support department.


Technical Specification

Technical Specification – Compressed Air System Fittings

NOTE: This specification refers principally, but not exclusively, to fittings from our Compressed Air range prefixed PM and MM. Other fittings, valves, tube and ancillary products have their own Technical Specification.

Product Selection and Installation

John Guest fittings and related products are specifically designed and manufactured by John Guest to the Technical Specification set out in the John Guest Product Catalogues. All John Guest fittings and related products should be selected, installed, used and maintained in accordance with these Technical Specifications. It is the customer’s/user’s responsibility to ensure that John Guest fittings and related products are suitable for their intended applications, are properly installed and maintained and are used in accordance with the Technical Specifications. It is also the customer’s/user’s responsibility to provide its own customers with all relevant technical information about John Guest products it supplies them. If you have any questions about our technical specifications, please contact us.

For use with chemicals or other potentially aggressive liquids, please refer to our Customer Services Department.

Super Speedfit fittings and related products are not recommended for use with explosive gases, petroleum spirits, and other fuels or for central heating systems.

Maintenance and Replacement Intervals

John Guest products generally require little maintenance but as a minimum we recommend routine visual inspection. Frequency of visual inspection will depend on severity of application and risk of failure. If after visual inspection John Guest products appear damaged, cracked, charred, discoloured, heat distorted or corroded they should be replaced. Any product that is or appears to be leaking should be replaced.

Product life is affected by the severity of the application, the hostility of the working environment and contact with aggressive chemicals or liquids. It is therefore important that specific replacement intervals be considered by specifiers/users/customers based on previous service life or when failure could result in unacceptable downtime, damage or injury risk.

Installation and System Testing

Fittings and tube should be kept clean and undamaged before use.

All tube and fittings installations must be pressure tested after installation to ensure system integrity before handing over to the final user. See also “How to make a connection”.

Working Temperature Range

Minimum Working Temperature = -20°C

Maximum Working Temperature = +70°C

The above is for use with air. For below 0°C please consult our Customer Services Department.

Working Pressure

The John Guest Compressed Air System is suitable for the following temperatures and pressures.

Temperature Pressure
+23°C 10 BAR
+70°C 7 BAR

The above ratings are for air. For use with other fluids or other tube or at other temperatures and pressures, please consult our Customer Services Department.

Pipe Types

John Guest fittings are intended for use with John Guest nylon pipe but are also suitable for use with a wide range of plastic and soft metal pipes including UPVC, ABS, Polyethylene, Nylon, mild steel and copper to the tolerances set out below. Soft plastic pipe, such as Nylon should have a minimum wall thickness of 1.5mm. The pipe must have a good quality surface and be damage free.

Pipe Tolerances

These John Guest fittings are intended for pipes with outside diameters to the following tolerances

Size 12mm to 28mm OD
Tolerance +0.05 to -0.10mm OD

Collet Covers

Are available as additional security against removal of the tube or to provide a simple means of colour coding. The cover is offered in a range of six colours.

Maximum Torque Values

The following maximum torque values should be applied.

Size 3/8″ 1/2″ 3/4″ 1″
Plastic threads 3.0Nm 3.0Nm 4.0Nm 4.0Nm
Metal threads N/A 4.0Nm 5.0Nm 5.0Nm

It is recommended that all installations are checked prior to use to determine that a seal has been made.

Do not overtighten plastic fittings as this could cause undue stress and eventual failure. Recommended torque figures are shown above and must be adhered to. John Guest recommend OEM customers consider replacing threaded ‘ports’ with the modern method of using John Guest Cartridge Systems.

Cleaners and Sanitising of Acetal Fittings

Our advice to customers is to use cleaners and sanitising agents that are above ph4 and low in hypochlorite levels. Acetal fittings and parts that are cleaned and/or sanitised should be rinsed immediately with copious amounts of clean tap water to remove all traces of the cleaners.

Details of which products are made from acetal are shown in our catalogues but generally John Guest products incorporating acetal are designated by the part number prefix PI, PM, CI, CM and RM. Polypropylene fittings offer greater resistance to aggressive chemicals than acetal fittings. Polypropylene does not have the same mechanical properties as acetal and John Guest polypropylene fittings are generally designated by the part number prefix PP and PPM.

Our material suppliers recommend ECOLAB Oasis 133 as a suitable cleaner for acetal products manufactured by John Guest.

Installations – Our Recommendations

The pressure rating and installation guidelines of the tubing involved must also be considered during the design of a compressed air system.

Pipe should be supported at minimum 800mm to prevent excessive load being applied to the fitting. These supports should not be closer than 25mm from the end of the fitting.

John Guest fittings and pipe should only be connected after the air receiver and not direct to a compressor.

We recommend collet covers be fitted when pipework is hidden inside walls and ceilings.

It is recommended that all pipe and fittings installations are pressure tested after installation and before handing over to the final user.


Whilst we give a warranty against defects in manufacture or materials, it is the responsibility of the specifier to ensure that fittings and related products are suitable for their application. The installation must be carried out correctly in accordance with our recommendations, complying with recognised codes of practice and relevant national standards, and be properly maintained. Please refer to our terms and conditions of sale.

The company has a policy of continuous research and development and reserves the right to amend without notice the specification and design of all products. John Guest reserve the right to change the colour and shape of products. Photographs are for illustration purposes only.

Flow Rates for Aluminium and Nylon Pipe

Pipe Size Nylon Pipe
Ring Main

Air Velocity

6M sec at 8 bar

Nylon Pipe
Ring Main

Air Velocity

6M sec at 8 bar

Pipe Ring Main

Air Velocity

6M sec at 8 bar

Aluminium Pipe

Air Velocity

15M sec at 8 bar

15mm 7.27 18.2
18mm 17.60 44.10 23.00 54.70
22mm 29.10 72.70 36.00 86.30
28mm 47.50 119.00 60.80 147.00

N.B. Quoted figures for ring main air flows can be doubled as flow is bi-directional


Installation Advice



Fittings and pipe should be kept clean and undamaged before use.

Cut the pipe square. We recommend the use of the JG Pipe Cutter.


DO NOT use a hacksaw. To avoid damage to the ‘O’ ring remove burrs and sharp edges.


Push up to pipe stop.

Pull to check secure. Test the system before use.


To disconnect, ensure the system is depressurised. Push the collet towards the fitting and remove the pipe. The fitting can be reused.

28mm fittings also have a collet with stainless steel teeth and an ‘O’ ring.

After inserting the pipe, a screw cap is turned approx 1/4 turn. This locks the collet in place and reduces lateral and sideways movement of the pipe.

To disconnect, turn the screw cap 1/4 turn, push in the collet and remove the pipe. The fitting and pipe can be reused.

Nylon, Copper & Aluminium Pipe

Whilst we recommend the use of John Guest Rigid Nylon Pipe, John Guest Fittings can also be used with copper or aluminium pipe.



Designed to simplify pipe connections in restricted spaces, the Stem Elbow gives an instant swivel fitting so a pipe can be orientated in any direction.


Can be used with an elbow to make ‘U’ turn connection.

Please note a collet cover cannot be used on a Speedfit end assembled with the stem of a 22mm Stem Elbow.

Can be used with a Tee.


The new Water Trap Tee from John Guest solves the on-going problem of moisture in acompressed air system and provides the easy alternative to the need to install “Swan Necks”.

The ingenious inside arrangement of the fitting allows air to flow, with minimum head loss, from the main to take-off point without allowing water to follow. The moisture is retained in the line to be drawn off at some suitable location.

It is of vital importance for the correct function of the Water Trap Tee that the air distribution system be nearly horizontal and that the outlet port be facing downwards.


The Water Trap Tee Convertor is a simple convenient way of converting a standard John Guest 28mm Tee to a Water Trap Tee.

This will stop condensing water entering the vertical take off spur.

The air supply needs to be installed with the correct fall and water drain points regularly vented.

To Assemble

Use either John Guest 28mm Nylon Pipe or 28mm copper pipe. The pipe to be cut square and be free of burrs.

Press the shorter spigot into the pipe. The fit on copper pipe will be loose, this will not affect the function.

Push the pipe and convertor up to the pipe stop of the centre leg of the tee.

Turn the screw cap approx 1/4 turn to lock the pipe in position.


The End Stop can be used to provide a permanent connection or a temporary shut off. Because it is easy to disconnect the fitting from the pipe, the End Stop can be put in place to be removed at a later date to allow a system to be extended or modified.